Phase shifted transmitted signals in a simultaneous dual polarization weather system

ABSTRACT

A system for simultaneously propagating dual polarized signals in a polarimetric radar system includes a system for shifting the phase of one of the two signals. The simultaneous dual polarization weather radar transmits signals in both the horizontal and vertical orientations at the same time. Upon reception, the signals in each channel are isolated and a number of standard and polarimetric parameters characterizing atmospheric conditions are determined. The accuracy upon which these parameters can be determined depends partially upon the interference between these two channels. The system and method isolates the vertical and horizontal channels by using the phase information from the signals to minimize the interference.

TECHNICAL FIELD

The present invention relates generally to weather radar systems.Particularly, the present invention relates to Doppler weather radarsystems utilizing dual polarization to enhance reflectivity resolutionsof liquid hydrometeors.

BACKGROUND OF THE INVENTION

The majority of weather radar systems in operation today utilize asingle polarization strategy to enhance precipitation reflectivity.Liquid hydrometeors (e.g. raindrops) deviate from a sphere when theirradius is greater than about 1 mm and have a shape more like that of anoblate spheroid with a flattened base (similar to a hamburger bun) thatgives a slightly stronger horizontal return. Hence, current radarsystems are typically horizontally polarized to enhance precipitationreturns.

However, singly polarized radar systems have severe limitations inregions with partial beam blockage and such systems do not facilitatehydrometeor classification. To overcome these shortcomings of singlypolarized weather radar systems, systems with alternating pulses ofhorizontally and vertically polarized signals have been developed. Thesedual polarized radar system, sometimes referred to as “polarimetricweather radars,” offer several advantages over conventional radars inestimating precipitation types and amounts. Foremost among theseadvantages are the capability to discriminate between hail and rain,detect mixed phase precipitation, and estimate rainfall volume.

Current dual polarized radar systems utilize polarization that isaltered sequentially between linear vertical and linear horizontal tocapture data enhancing values, such as, for example: (1) reflectivityfactors at both horizontal and vertical polarization; (2) differentialreflectivity for two reflectivity factors; (3) cumulative differentialphasing between the horizontally and vertically polarized echoes; (4)correlation coefficients between vertically and horizontally polarizedechoes; and (5) linear depolarization ratios. In addition, Dopplervelocity and spectrum width can be obtained by suitably processing thehorizontally and vertically polarized return signals.

Dual polarized radar systems also allow for the implementation ofprecipitation classification schemes from inference radar processing ofhydrometeor shapes as discussed in various papers authored bypractitioners who work in these areas, such as, Ryzhkov, Liu,Vivekanandan, and Zrnic. In addition, by looking at phase differencesbetween the horizontal and vertical components, the effects of partialbeam blockage can be mitigated and greater clutter rejection can beobtained. However, the underlying assumption is that subsequent pulses(those of each polarization) are highly correlated and provide aneffective velocity range reduced by a factor of two.

Another limitation of current alternating dual polarization radarsystems is long dwell times and velocity range reductions. Any receivedreflection signal resulting from either polarization modes is assumed tocome from the same scatterers (e.g. hydrometeors). In order to correlatethe data from both the horizontally polarized and vertically polarizedchannels in current systems utilizing a waveguide switch, a singlepolarization pulse is transmitted followed by a period of delay (thedwell time) while reflections signals are being received. The opposingpolarity pulse is subsequently sent and additional data is received bythe same (single) receiver chain during a second dwell time. Receptionof reflection signals, therefore, occurs during these two dwell periodsduring antenna rotation within a single beamwidth, resulting in a longertotal dwell time for each beamwidth interrogation. Similarly, since thedwell time for each beamwidth interrogation (vertical+horizontal) isdoubled, computational velocity perception is halved, thereby limitingthe ability of current systems to resolve relatively high windvelocities in radar returns.

Improved dual polarization weather radar systems use simultaneous dualpolarization modes to solve issues such as long dwell times and velocityrange reductions instead of alternating polarization modes. Dualpolarized systems, which propagate both a horizontal and aperpendicularly vertical wave simultaneously, have additional problemsrelating to the interference between the horizontal and verticalcomponent. As shown in FIG. 1A, a dual polarized simultaneous wave 10has a horizontal component 12 and a vertical component 14. The twocomponents are characterized by their amplitudes and the relative phasebetween them. When viewed along the direction of propagation, the tip ofpropagated wave vector of a fully polarized wave traces out a regularpattern of an ellipse. The shape of the ellipse is governed by themagnitudes and relative phase between the horizontal 12 and verticalcomponents 14 of the wave. As the dual polarized elliptical wave 10 hitsa reflective surface, the reflective surface can change the polarizationof the wave 10 as it is reflected to be different from the polarizationof the wave as it propagates. The radar antenna may be designed toreceive the different polarization components of the wave 10simultaneously. For example, the H and V (horizontal and vertical) partsof an antenna can receive the two orthogonal components of the reflectedwave.

A radar system using H and V linear polarizations can thus have thefollowing signals (or channels): HH—for signals that are horizontaltransmit and horizontal receive, VV—for signals that are verticaltransmit and vertical receive, HV—for signals that are horizontaltransmit and vertical receive, and VH—for signals that are verticaltransmit and horizontal receive. The HH and VV combinations are referredto as like-polarized, because the transmit and receive polarizations arethe same. The HV and VH channels are cross-polarized because thetransmit and receive polarizations are orthogonal to one another. Thecross-polarized signals are created from a reflection that is notaligned perpendicularly with the direction of the propagation. As thereflection returns to the antenna at an angle other than parallel to thepropagated angle, a portion of the horizontal signal results in avertical component, and vice versa.

By examining the four signals, HH, VV, HV, and VH, all of theinformation necessary to describe the reflective source is captured. Byexamining the relative angle between the different signals and the powerof the signals, the reflective source may be identified. The dualpolarized radars of today, however, are unable to isolate and capturethe different signals if the horizontal and vertical propagating signalsare sent simultaneously.

SUMMARY OF THE INVENTION

An object of the invention provides a radar system comprising a waveformgenerator, amplifiers, an antenna and a receiver. The waveform generatoris configured to generate a first signal and a second signal. The firstsignal having a different phase from the second signal. The amplifiersare configured to amplify the first and second signals. The antenna isconfigured to simultaneously propagate the amplified first signal in afirst plane and the amplified second signal in a second plane angularlyrotated from the first plane. The receiver is configured to receive afirst reflected signal having the phase of the first signal and a secondreflected signal having a phase of the second amplified signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are diagrams of a prior art propagation signal for asimultaneous dual polarization radar system having a horizontal andvertical signal;

FIG. 2 is a diagram of one embodiment of a simultaneous dualpolarization radar system;

FIG. 3 is another diagram of one embodiment of a simultaneous dualpolarization radar system; and

FIG. 4 is a block diagram of the steps performed in one embodiment ofthe simultaneous dual polarization radar system.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to the drawings, FIG. 2 shows a diagram of an embodiment of asimultaneous dual polarization radar system 20. An arbitrary waveformgenerator 22 generates an arbitrary waveform for the vertical andhorizontal components at an intermediate frequency (IF) less than thetransmitting frequency. The waveform in the arbitrary waveform generator22 is passed to mixers 24A and 24B which combine the arbitrary waveformswith a stable local oscillator signal generated in a stable localoscillator 26. Amplifiers 28A and 28B amplify the signal from the mixers24A and 24B and send the signals to an orthogonal feedhorn and antenna30 for transmission.

The antenna and feedhorn 30 receive a scattered signal and transmit ahorizontal and vertical scatter signal for processing in the radarsystem 20. Mixers 32A and 32B mix the vertical and horizontal componentswith the local stable oscillator signal from the local stable oscillator26 to remove the local stable oscillator signal from the scatter signal.IF filters 34A and 34B filter the scattered IF signals based on thearbitrary waveform from the arbitrary waveform generator 22 and filterthe signal to remove all signal contributions outside a tight range offrequencies centered around the intermediate frequency. The digitalreceiver board 36 receives the filtered scattered signal and thearbitrary waveform and transforms the filtered scattered signals intothe baseband in-phase and quadrature signals for data processing.

The arbitrary waveform generator 22 may create an arbitrary waveform foreach of the horizontal and vertical signals at an intermediate frequencyless than the transmitting frequency. While the arbitrary waveformgenerator 22 may create an arbitrary signal for both the horizontal andvertical signals, the arbitrary waveform generator 22 may also createonly one arbitrary waveform for only one of the horizontal and verticalsignals. Whether one or two arbitrary waveforms is generated may bedetermined by a user who may access the arbitrary waveform generator 22.When the horizontal and vertical signals are propagated, both signals donot need to be modulated.

The arbitrary waveform generator 22 may capture a ‘real world’ signalusing a DSO or digitizer, may create the waveform from a mathematicalformula, may create the waveform graphically using drawing tools, or mayconstruct the waveform from a library of waveform shapes. The arbitrarygenerator may use any of these methods, or a combination of thesemethods to create a waveform. As will be described later, it ispreferred that the arbitrary waveform generator 22 creates a pair ofsignals that are orthogonal to each other to maximize the cross polarindependence of the horizontal and vertical signals.

The arbitrary waveform generator 22 may include some level of built-inwaveform editing such as point-by-point value insertion, straight lineinterpolation between points or standard waveform insertion betweenpoints. However, complex arbitrary waveforms are more likely createdoutside of the generator and downloaded via the digital interfaces inthe arbitrary waveform generator 22. The arbitrary waveform generator 22creates the horizontal and vertical signals and sends these signals tothe mixers 24A and 24B to combine the arbitrary waveform with a stablesignal that when combined with the arbitrary waveform creates a signalhaving a frequency desired for transmission.

In one embodiment, the arbitrary waveform generator 22 also sends thearbitrary waveform to the IF Filters 34A and 34B. The arbitrary waveformgenerator 22 provides the arbitrary signal so that the IF filters 34Aand 34B may filter higher frequency components from the received signalto a narrow frequency band centered at the IF frequency. In anotherembodiment, the IF filters 34A and 34B may filter the higher frequencycomponents from the received signal to a narrow frequency band centeredat the IF frequency without first receiving the arbitrary waveform fromthe IF filters 34A and 34B. Once the IF filters 34A and 34B havefiltered the higher frequency components from the received signal, thefiltered signal components are passed to the digital receiver board 36.

The arbitrary waveform generator 22 also passes the arbitrary waveformto the digital receiver board 36 so that the digital receiver board 36may digitize the received IF signal and transform it into the basebandin phase and quadrature signals. The received, baseband filtered signalcontains the characteristics of the hydrometeors that reflected thetransmitted signal. As will be described below, the characteristics ofthe arbitrary waveform allow all of the polarimetric data to beretrieved in a simultaneous dual polarization weather radar system.

The stable local oscillator 26 generated a stable, low noise referencesource at a frequency equal to the transmitted frequency minus theintermediate frequency of the arbitrary waveform. The signals are mixedto produce a signal at the transmitted frequency. Generally, the signalfrom the local oscillator 26 is a carrier signal that is combined withthe arbitrary waveform to form a horizontal signal unique to thevertical signal, but both signals having a transmitting frequencydesirable for weather identification.

The signal from the oscillator 26 is also injected into the mixers 32Aand 32B with the received signal from the antenna 30 in order toeffectively change the received signal by heterodyning it to produce thesum and difference of that received signal. The difference signal willbe at the intermediate frequency of the arbitrary waveform, plus orminus any doppler shift in the received signal. Thus removing thestable, oscillating signal from the received signal. The received signalis then passed at a frequency close to the intermediate frequency to theIF filters 34A and 34B.

The amplifiers 28A and 28B receive the signal from the mixers 24A and24B and amplify the signals to the power level desired for transmission.In this power amplifier embodiment, the amplifiers may be klystrons,TWTs, or other MOPAs. The size of the amplifiers 28A and 28B determinesthe maximum distance the transmitted signal can detect a reflector. Thegreater the amplification, the greater the distance a reflector may bedetected. The amplifiers 28A and 28B feed the amplified signal to theorthogonal horn and antenna 30 for transmission.

The horn 30 transmits the signal out as a pair of orthogonal signals(the horizontal signal and the vertical signal) in the elliptical shapedescribed in FIG. 1. When the horn 30 receives a reflected signal, itpasses the horizontal received signal to mixer 32A and the verticalreceived signal to mixer 32B. As previously discussed, these mixers 32Aand 32B downconvert the received signals with the local oscillatorsignal to beat a signal at the intermediate frequency for processing bythe IF filters 34A and 34B.

The IF filters 34A and 34B receive the downconverted signal and use thearbitrary waveform to form the baseband signals for processing. The IFfilter is tuned by the arbitrary waveform to remove all frequenciesoutside of a tight range of frequencies centered around the intermediatefrequency. Thus, the IF filters 34A and 34B are passed the arbitrarywaveform so that the IF filters 34A and 34B may set the intermediatefrequency which creates the bandpass IF filter. Once the signal isfiltered, and the signal left consists of the received horizontal andvertical arbitrary waveforms, then the signals are passed to the digitalreceiving board 36 for processing.

The digital receiving board 36 takes the horizontal and verticalreceived signals and generates the baseband in-phase and quadraturesignals (I and Q signals.) These signals are the signals that determinethe size, type, and direction of hydrometeors by giving the phase,frequency and amplitude of the received signals. The digital receiverboard 36 takes the signals from the IF filters 34A and 34B and comparesthe information in those signals with the information in the arbitrarywaveforms to calculate the I and Q signals of the received signals. Asdiscussed below, the type of arbitrary waveforms generated in thearbitrary waveform generator 22 are chosen so that when the digitalreceiving board 36 captures the received signal, the board 36 canisolate the horizontal and vertical components (HH and VV) from thecross components (HV and VH).

The arbitrary waveforms are made up of a set of data values againsttime. A waveform could be captured from a ‘real world’ signal using aDSO or Digitizer. Alternatively, a waveform could be created from amathematical formula, created graphically using drawing tools, or couldbe constructed from a library of waveform shapes. The arbitrary waveformgenerator 22 may use any of these of these methods. The arbitrarywaveform generator 22 generates a pair of signals, a horizontal signaland a vertical signal, to send to the mixers 24A and 24B. Thetransmitted signal, then, may be characterized as a combination of thesevertical and horizontal signals, or mathematically:S _(T) =H _(T){circumflex over (H)}+V _(T){circumflex over (V)}

-   where S_(T) is the transmitted signal;-   H_(T) is the amplitude of the horizontally transmitted signal, as    amplified in amplifier 28A;-   H is the horizontal vector;-   V_(T) is the amplitude of the vertically transmitted signal, as    amplified in amplifier 28B; and-   V is the vertical vector.

The received signal will have a similar form, having a vertical andhorizontal component, or mathematically:S _(R) =H _(R){circumflex over (H)}+V_(R){circumflex over (V)}

-   where S_(R) is the received signal;-   H_(R) is the amplitude of the reflected horizontal signal;-   H is the horizontal vector;-   V_(R) is the amplitude of the reflected vertical signal; and-   V is the vertical vector.

The received signal, however, in each polarization, is a combination ofthe horizontal and vertical transmitted signals. As previouslydiscussed, this is because when the transmitted signal is reflected, thesignal rotates. When this occurs, the orthogonal projections of thesignal to the H and V vectors include components from both thehorizontally transmitted and vertically transmitted signals.Mathematically, the two received signals can be described as:H _(R) =αH _(T) +βV _(T) and V _(R) =δH _(T) +γV _(T)Where α, β, δ, γ are scalars related to the angular rotation of thehorizontal and vertical signals and the proportion of the signal that isreflected back to the antenna 30. Thus, the scattering matrix of thereceived signal may be expressed as:

$\begin{bmatrix}\alpha & \beta \\\delta & \gamma\end{bmatrix}$

and the matrix equation describing the received signal as a function ofthe transmitted signal may be expressed as:

$\begin{bmatrix}H_{R} \\V_{R}\end{bmatrix} = {\begin{bmatrix}\alpha & \beta \\\delta & \gamma\end{bmatrix}\begin{bmatrix}H_{T} \\V_{T}\end{bmatrix}}$

The elements in the scattering matrix determine the cross polar receivedsignal from the reflector. The diagonal terms are the amplitudes of thecopolarized signals corresponding to the two transmitted polarizations,and the off-diagonal terms are the amplitudes of the cross-polarizedsignals. As can be seen in the equations, the ability to calculate thescalars determines whether good estimates for the horizontal andvertical components can be determined, which are the quantities desiredfor extrapolation of the base moment estimates.

Generally, either the horizontal, vertical or both signals may beshifted. The horizontal and vertical signals may not be shifted with thesame phase information, because then the horizontal and vertical signalswould again be identical. As long as four samples are taken from thereceived signal, a definite solution for the scattering matrix may befound. It may be possible to solve the scattering matrix using lesssample points given the constraints of the system. Thus, because thescalars cannot exceed a value of 1, and the scalars for the horizontalsignal, α and δ, are related through the rotation angle of thehorizontal signal and the scalars for the vertical signal, β and γ, arerelated through the rotation angle of the vertical signal. Such that,α=H_(Rot) cos θ and δ=H_(Rot) sin θ

-   where H_(Rot) is the rotated, received horizontal signal; and-   θ is the angle of rotation of the horizontal signal.

Similarly, the scalars for the vertical signal may be expressed as,β=V_(Rot) cos φ and γ=V_(Rot) sin φ

-   where V_(Rot) is the rotated, received vertical signal; and-   φ is the angle of rotation of the vertical signal.

The rotated signals H_(Rot) and V_(Rot) are attenuated transmittedsignals. The amplitude of H_(Rot) and V_(Rot) is less than the amplitudeof the transmitted signals. Thus, H_(Rot) and V_(Rot) are constrained tobe less than the amplitude of the original signal. Using thisconstraint, as well as the angular relationships between α and δ and theangular relationship between β and γ, it may be possible to solve thescattering matrix using less than four samples from the received signal.

The rotated signals H_(Rot) and V_(Rot) may also be frequencies shiftedwhen received. One source of frequency shift occurs from the dopplereffect of a moving weather system. As the weather system moves relativeto the weather radar system, the rotated signals H_(Rot) and V_(Rot) maybe shortened (i.e., shift to a higher frequency) or may be lengthenedthereby being received at a lower frequency. Another frequency shift mayoccur because of the size asymmetry of a raindrop with respect to thehorizontal and vertical planes. Because the raindrop elongates in thehorizontal plane, there may be a shift in the horizontal plane. Bymeasuring the frequency shift and accounting for the relative change infrequency between the horizontal and vertical frequencies, thecontributions of the horizontal and vertical transmitted signals may beisolated within the weather radar system 10.

In a preferred embodiment, the arbitrary waveform generator 22 generatesa pair of signals that are phase shifted such that the signals areorthogonal to each other. One of the orthogonal signals is sent on thehorizontal transmission path and the other signal on the verticaltransmission path. By defining two functions that are orthogonal, thecomponents of the horizontal signal contributed through the verticallytransmitted signal and the components of the vertical signal contributedthrough the horizontally transmitted signal may be isolated in thereceived signals so that the horizontal and vertical components arecompletely recovered. Mathematically,H _(R)=Ψ_(H) αH _(T)+Ψ_(V) βV _(T) and V _(R)=Ψ_(H) δH _(T)+Ψ_(V)γ_(R) V_(T)

Where Ψ_(V) and Ψ_(H) are the phase shifting for the horizontal andvertical signals. When the signals are phase shifted, the signals willobey these equations:

∫_(a)^(b)Ψ_(V)(t)Ψ_(H)(t)𝕕t = 0 and Ψ_(H)⁻¹Ψ_(V) = Ψ_(V)⁻¹Ψ_(H) = 0

the signals can be used to reduce the equations in the scattering matrixto single equations as opposed to a system of equations that aresimultaneously solved in matrix form.

Using the properties that:

${\int_{a}^{b}{{\cos(t)}{\sin(t)}{\mathbb{d}t}}} = {{0\mspace{14mu}{and}\mspace{14mu}{\cos(t)}} = {\sin\left( {t - \frac{\pi}{2}} \right)}}$the phase shifting should be:|Ψ_(H)−Ψ_(V)|=π/2When the phase shifts in the horizontal and vertical signals are passedthrough the two equations for received horizontal and vertical signals,the equations simplify to:H_(R)=βV_(T) and H_(R)=αH_(T)andV_(R)=γV_(T) and V_(R)=δH_(T)when the signal is sampled at times equal to π/2, π, 3π/4, and 2π of thecycle of one transmitted signal. V_(T), H_(T), V_(R), H_(R), are allknown, the scalars in the scattering matrix may be determined from thesefour equations. Thus, in the case of orthogonally shifted horizontal andvertical signals, the processing required to determine the scatteringmatrix is minimized.

Turning now to FIG. 3, FIG. 3 shows another diagram of a simultaneousdual polarization radar system 40 using a single transmitter. A stablelocal oscillator 42 generates a stable local oscillator signal. A powercomponent 44 amplifies the stable local oscillator signal. A powerdivider 46 splits the amplified signal into two identical signals. Highpowered waveguide components 48A and 48B modulate the signal with onearbitrary waveform for the vertical and one arbitrary waveform for thehorizontal component. An orthogonal feedhorn and antenna 50 transmit themodulated signal into air.

Similar to the system of FIG. 2, the antenna and feedhorn 50 receive thescattered signal and transmit a horizontal and vertical scatter signalfor processing in the radar system 40. Mixers 52A and 52B mix thevertical and horizontal components with the local stable oscillatorsignal from the local stable oscillator to remove the local stableoscillator signal from the scatter signal. IF filters 54A and 54B filterthe scattered IF signals to a narrow frequency band centered at the IFfrequency. A digital receiver board 56 receives the filtered scatteredsignal and the signal modulation and processes the baseband in-phase andquadrature signals for data processing.

Many of the parts in the power oscillation radar system 40 behave in thesame manner as the similar components in FIG. 2. The processing of thescattered signal is the same, and includes all of the same components.The difference in the systems of FIG. 2 and FIG. 3 is the difference inthe generation of the transmitted signal. Both systems use a stableoscillator to form a portion of the transmitted signal and an orthogonalfeed horn and antenna to propagate orthogonal vertical and horizontalcomponents. The power component 44 of FIG. 3 may be a power amplifiersuch as that of a MOPA system or, in a different embodiment, a poweroscillator such as a magnetron. In a MOPA system, the stable localoscillator 42 passes the signal for amplification to a power amplifier.In a power oscillator system, the stable local oscillator 42 generates asignal at a frequency equal to the transmitted frequency minus the IFfrequency. The signal from the stable local oscillator 42 is mixed withthe received signal to produce the IF frequency signal.

Other components are generally similar but are used slightlydifferently. In the single transmitter simultaneous dual polarizationradar system of FIG. 3, such as a magnetron based system, the shiftedsignal is not introduced into the system until after the amplification.In the dual transmitter power amplifier system of FIG. 2, the referencesignal is modulated prior to amplification. Where a pair of amplifiersare used in the power amplifier system, only one amplifier is used inthe power amplifier system. Additionally, the single transmitter system40 includes a power divider 46 and a pair of power waveguide components48A and 48B.

The power divider 46 takes the single, amplified signal from theamplifier or power oscillator 44 and divides the signal into twoidentical signals. Because the power is halved for each signal, the highpower component 44 outputs a signal that is larger than the amplifiersin FIG. 2 to meet the same power specifications for the antenna. The twoidentical wave signals leave the power divider 46 and enter the highpower waveguide components 48A and 48B.

The high power waveguide components 48A and 48B shift the identicalsignals similar to the function of the arbitrary waveform generator inFIG. 2. The high power waveguide components 48A and 48B (which are highpowered shifting devices) may be a resonant cavity that shifts the waveaccording to the desired shifting. In one embodiment, the shift may begenerated within the receiver 56 or a signal processor. The shift mayalso be preprogrammed into high power shifting devices 48A and 48B ormechanically based on the structure of the preprogrammed devices.

While the embodiment of FIG. 3 uses a pair of high power shiftingdevices 48A and 48B, another embodiment may only have a single highpower shifting device. With a single high power shifting device, one ofthe signals would be shifted and the other signal would be left alone.The signal modulated may be either the vertical or horizontal signal.Regardless whether one or two high power shifting devices 48A and 48Bare used, the shifted signal from the high power devices 48A and 48B arealso sent to the receiving elements which process the received signal.

The shifted signal is sent to the IF filters 54A and 54B as well as thedigital receiving board 56. Similar to the configuration of FIG. 2, theIF filters 54A and 54B filter the received signal to a narrow frequencyband around the IF frequency for processing in the digital receivingboard 56. The digital receiving board 56, as discussed above, uses theshifted signal from the high power devices 48A and 48B to process thefiltered IF signal from the IF filters 54A and 54B. In this manner, theshifted signal from the high power devices 48A and 48B serve as thetransmitted horizontal and vertical signals for processing.

Turning now to FIG. 4, FIG. 4 is a block diagram of the steps performedin one embodiment of the simultaneous dual polarization radar system.The method starts in Step 60. Horizontal and vertical pulses aregenerated in step 62. The horizontal and vertical signals are shifted instep 64. In step 66, the shifted signals are transmitted. The verticaland horizontal scattered signals are received by the radar system instep 68. The vertical and horizontal signals are downconverted in step70 to remove a stable oscillating signal from the received signal sothat the intermediate frequency signal is left. The IF signal istransferred in step 72 and processed to the baseband signals in step 74.The baseband signals are sent to a signal processor in step 76 anddecoded in step 78 using the shifting from the transmitted signal todetermine the values within the scattering matrix. The vertical andhorizontal received signals are isolated and the polarimetric data iscalculated in step 80. The method ends in step 82.

By implementing the method of FIG. 4, a polarimetric radar system maysimultaneously send vertical and horizontal components in a transmittedsignal and isolate the vertical and horizontal components to process thedata received in both the horizontal and vertical components resolvedusing signals in both the horizontal and vertical planes. The methodalso decreases the long dwell times of polarimetric radar systems whichswitches between sending a single horizontal or vertical signal. Byusing a simultaneous dual system, the velocity characteristics of thereflectors may also be resolved with higher specificity because thedelay between receiving like signals is halved.

While the invention has been shown in embodiments described herein, itwill be obvious to those skilled in the art that the invention is not solimited but may be modified with various changes that are still withinthe spirit of the invention.

1. A radar system, comprising: a. a sole arbitrary waveform generatorconfigured to generate a first signal and a second signal, said firstsignal having a different phase from said second signal; b. a pair ofsignal mixers, one said signal mixer electrically coupled to an outputof said waveform generator and said other mixer electrically coupled toan output of said waveform generator; c. a local oscillator electricallycoupled to said pair of signal mixers such that said first and secondsignals are heterodyned with a signal from said local oscillator; d. apair of amplifiers configured to amplify the output from said pair ofsignal mixers; e. a single orthogonal horn and antenna assembly coupledto said pair of amplifiers and configured to simultaneously propagatesaid amplified and heterodyned first signal in a first plane and saidamplified and heterodyned second signal in a second plane angularlyrotated from said first plane; f. a second pair of mixers electricallycoupled to and arranged with said orthogonal horn and antenna assemblysuch that said second pair of mixers receives orthogonally orientedreflectivity signals received from said horn and antenna assembly,wherein each of said second pair of mixers is electrically coupled tosaid local oscillator such that said second pair of mixers mixes saidorthogonally oriented reflectivity signals with said local oscillatorsignal; g. a pair of intermediate frequency filters each coupled to oneof said second pair of mixers; and, h. a receiver coupled to both ofsaid intermediate frequency filters, said receiver including means forresolving the scattering matrix associated with said orthogonallyoriented received reflectivity signals and wherein said resolving meansis configured to produce polarimetric data from reflectivity signalshaving a phase of said first signal and reflectivity signals having aphase of said second signal.
 2. The radar system of claim 1, whereinsaid resolving means further comprises means to calculate the phaserelationship between the first and second signals in accordance with theequation:|Ψ_(H)−Ψ_(V)|=π/2.
 3. The radar system of claim 1, wherein saidarbitrary waveform generator is configured to shift said first signalorthogonally relative to said second signal at random intervals.
 4. Theradar system of claim 1, wherein said arbitrary waveform generator isconfigured to generate a first arbitrary waveform comprising said firstsignal and a second arbitrary waveform comprising said first signal,each waveform formed at an intermediate frequency less than thefrequency of said propagated first and second signals, and wherein saidwaveform generator is further configured such that said first and secondarbitrary waveforms are different from one another.
 5. The radar systemof claim 1, wherein said receiver is further configured to receive saidfirst and second signals from said waveform generator.
 6. The radarsystem of claim 5, wherein said receiver includes means for isolatingsaid first and second reflected signals by comparing said first andsecond received signals to said first and second signals received fromsaid waveform generator.
 7. The radar system of claim 6 wherein: a. saidorthogonal horn and antenna assembly is further configured to receive afirst planar signal including a portion of said first reflected signaland a portion of said second reflected signal; b. said orthogonal hornand antenna assembly is further configured to receive a second planarsignal including a portion of said first reflected signal and a portionof said second reflected signal; and c. said receiver is furtherconfigured to calculate an angular rotation of said first and secondreflected signal from said first and second plane.
 8. A method forprocessing simultaneous dual polarized signals from a radar system,comprising the steps of: a. generating horizontal and vertical pulses;b. shifting said vertical pulse signals relative to said horizontalpulse signals such that said signals have disparate phases; c. mixingsaid shifted signals with a local oscillator signal; d. propagating saidmixed vertical and horizontal pulse signals through an orthogonal hornand antenna assembly into space; e. receiving a first signal from areflected source, said first received signal including a portion of saidmixed vertical pulse signal and a portion of a said mixed horizontalpulse signal, wherein said vertical pulse signal is shaped differentlythan said horizontal pulse signal; f. receiving a second signal from areflected source, said second received signal including a portion ofsaid first mixed vertical pulse signal and a portion of said mixedhorizontal pulse signal; and g. decoding said first and second receivedsignals by comparing said first mixed vertical pulse signal and saidmixed horizontal pulse with said first and second received signals. 9.The method of claim 8, further comprising the step of comparing saidsecond transmitted signal with said first and second received signals.10. The method of claim 9, further comprising receiving said first andsecond received signals simultaneously.
 11. The method of claim 8wherein said first transmitted signal is orthogonal to said secondtransmitted signal.
 12. The method of claim 11, wherein said firsttransmitted signal and said first received signal are located in a firstplane and said second transmitted signal and said second received signalare located in a second plane.
 13. The method of claim 12, wherein saidfirst plane is orthogonal to said second plane.
 14. A radar systemcomprising: a. a sole local oscillator configured to generate a lowpower signal; b. an amplifier configured to amplify said low powersignal to a high power signal; c. a power divider configured to splitsaid high power signal into a first signal and a second signal; d. ahigh powered shifting device configured to shift said first signal; e.an orthogonal horn and antenna assembly coupled to said power dividerand configured to simultaneously propagate said first signal in a firstplane and said second signal in a second plane angularly rotated fromsaid first plane, wherein said first plane is orthogonal to said secondplane; and f. a second pair of mixers electrically coupled to andarranged with said orthogonal horn and antenna assembly such that saidsecond pair of mixers receives orthogonally oriented reflectivitysignals received from said horn and antenna assembly, wherein each ofsaid second pair of mixers is electrically coupled to said localoscillator such that said second pair of mixers mixes said orthogonallyoriented reflectivity signals with said local oscillator signal; g. apair of intermediate frequency filters each coupled to one of saidsecond pair of mixers; and, h. a receiver coupled to both of saidintermediate frequency filters, said receiver including means forresolving the scattering matrix associated with said orthogonallyoriented received reflectivity signals and wherein said resolving meansis configured to receive a first reflected signal having the shape ofsaid first signal and a second reflected signal having a shape of saidsecond signal.
 15. The radar system of claim 14, wherein said receiverfurther comprises means to calculate the phase relationship between thefirst and second signals in accordance with the equation:|∩_(H)−∩_(V)|=π/2.
 16. The radar system of claim 14, wherein said localoscillator is configured to shift said first amplified signal from saidsecond amplified signal.
 17. The radar system of claim 14, furthercomprising a second high powered shifting device configured to shiftsaid second amplified signal wherein said oscillator generates saidfirst and second signals at an intermediate frequency less than thefrequency of said propagated first and second signals.
 18. The radarsystem of claim 14, wherein said first and second phase shifts are sentto said receiver.
 19. The radar system of claim 14, wherein saidreceiver is coupled to said high powered shifting and further configuredto receive said phase shifts from said high powered shifting device. 20.The radar system of claim 19, wherein said receiver isolates said firstand second reflected signals by comparing said first and second receivedsignals to said phase shift.
 21. The radar system of claim 20 wherein:a. said orthogonal horn and antenna assembly is further configured toreceive a first planar signal including a portion of said firstreflected signal and a portion of said second reflected signal; b. saidorthogonal horn and antenna assembly is further configured to receive asecond planar signal including a portion of said first reflected signaland a portion of said second reflected signal; and c. said receiver isfurther configured to calculate an angular rotation of said first andsecond reflected signal from said first and second plane.
 22. A methodfor propagating simultaneous dual polarized signals from a radar system,comprising the steps of: a. generating a first signal and a secondsignal; b. shifting said first signal such that said first signal andsaid second signal are phased differently; c. heterodyning said firstand second signals with a local oscillator; and, d. propagating saidfirst signal on a first plane and said second signal on a second planethrough an orthogonal horn and antenna assembly into space, wherein saidsecond plane is rotated from said first plane.
 23. The method of claim22, wherein said first plane is orthogonal to said second plane.
 24. Themethod of claim 22, further comprising propagating said first and secondsignals simultaneously.
 25. The method of claim 22 wherein said firstsignal is orthogonal to said second signal.
 26. The method of claim 25,wherein said first signal and a first received signal are located insaid first plane and said second signal and a second received signal arelocated in said second plane.
 27. The method of claim 26, wherein saidfirst plane is orthogonal to said second plane.
 28. The method of claim27, further comprising: a. decoding said first and second receivedsignals by comparing said first signal with said first and secondreceived signals, b. wherein said first received signal includes aportion of a first transmitted signal and a portion of a secondtransmitted signal; and c. said second received signal includes aportion of said first transmitted signal and a portion of said secondtransmitted signal.
 29. The method of claim 28, further comprising thestep of comparing said second transmitted signal with said first andsecond received signals.
 30. The method of claim 29, further comprisingreceiving said first and second received signals simultaneously.